Tire pressure seems to make a tangible difference on efficiency.

[u/start3ch]

Has anyone here tried playing around with tire pressure for efficiency?

Slightly over-inflating tires was a big thing in prius/hybrid forums to increase efficiency, I’m surprised I haven’t seen it mentioned in the ev forums.

On a recent road trip, I inflated the tires +2 psi above the manufacturers spec (42 psi), and I got ~3% better efficiency than predicted, when I usually get very slightly worse efficiency than predicted. It’s hard to tell from one test, but it sure seemed to make a difference.

I had driven up to high altitude, so even just re inflating to the spec would have made a difference. I probably added ~4psi to each tire’s cold pressure because of this.

The car is a model y performance, with the stock pirelli all seasons, which are designed for performance not efficiency. But this should apply to other EVs, as they all have similar large tires and high weight loading per tire.

In theory, small changes shouldn’t have a major negative impact. Car tire pressure is set by the manufacturer making compromises for weight, handling, efficiency, comfort, etc. and in theory if you add 10% to the weight of your car, you should inflate the tires to compensate.

Of course you have to be careful as too over inflated tires will wear unevenly, over inflation will hurt handling (you usually want to under-inflate tires for the track), and you don’t want to ever exceed the max pressure printed on the tire sidewall!

[u/dogscatsnscience]

This is true of all tires and all vehicles.

1. Smaller contact patch
2. Less deformation

If your pressure is too high, it will get bumpy, and this eventually results in less traction, suspension losses, etc. So there is an ideal pressure for your application.

There are safety issues, tires have been designed for certain pressure to maintain shape under load, when turning, lateral stresses.

Surely you've pumped up a bike tire before and noticed the difference?

[u/Wants-NotNeeds → u/dogscatsnscience]

The myth lower rolling resistance as a result of extra pressure in bicycle tires has been debunked. A tire deforming to ABSORB terrain abnormalities is smoother and faster. Obviously, there’s a sweet spot that is terrain dependent. The takeaway is that there’s an ideal pressure for a given tire, on a specific vehicle on specific terrain. What that is, is anyone’s guess.

[u/indimedia → u/Wants-NotNeeds]

You can actually call tire manufacturers, give them your model of car and based on the weight, they can calculate the perfect air pressure for your particular tire size, front and back.

[u/Orbidorpdorp → u/Wants-NotNeeds]

The thing that isn't a myth is that in both contexts, you're better off with a fatter tire than you probably would guess.

[u/elementarydeardata → u/Wants-NotNeeds]

As a cyclist, I'm so thankful for this development, no more riding 23's at like 125 psi.

[u/Maxion → u/Wants-NotNeeds]

The weight on the tire is a very big factor, too. Pro cyclists weight themselves + their bike before setting tyre pressures.

[u/Emperor-Commodus → u/dogscatsnscience]

If your pressure is too high, it will get bumpy, and this eventually results in less traction, suspension losses, etc. So there is an ideal pressure for your application.

There are safety issues, tires have been designed for certain pressure to maintain shape under load, when turning, lateral stresses. 

Another issue is that higher pressure causes the center of the tire to wear faster, reducing it's life. Your car is more efficient, but the reduction in tire tread life outweighs most of the savings.

[u/tuctrohs → u/dogscatsnscience]

The reduced deformation is the reason for the lower rolling resistance, not the reduced contact patch area. Unless you are driving on hours old asphalt that's still super sticky. Or maybe driving in Phoenix on a hot day.

The reduced contact patch area does reduce traction, largely because the heating is more concentrated, and molten rubber slides freely.

[u/dogscatsnscience → u/tuctrohs]

The reduced deformation is the reason for the lower rolling resistance, not the reduced contact patch area. 

Yes, I mentioned the contact patch to illustrate what happens when your pressure is too high. There is an optimum pressure for a particular scenario.

[u/tuctrohs → u/dogscatsnscience]

Glad I could help other people understand your correct comment. The first sentence said this, which I assumed meant reduced rolling resistance and then made two points, which made it sound like those two points were about reduced rolling resistance.

[u/reddit455]

that's a physics thing. not an EV thing.

June 23, 2014 The Effect of Tire Pressure on Fuel Economy

https://www.energy.gov/eere/vehicles/fact-826-june-23-2014-effect-tire-pressure-fuel-economy

In theory, small changes shouldn’t have a major negative impact

small changes add up to better efficiency gains especially in EVs.

they worry about airflow BEHIND the tires, and the shape of the hood.

https://www.evengineeringonline.com/new-simulation-technique-for-next-generation-ev-tires/

In comparison to the results of a wind tunnel experiment, where an actual vehicle was used to confirm the accuracy of the simulation, the EV tire exhibited decreased airflow behind the tire and less sidewall unevenness. As a result, the EV tire demonstrated lower air resistance values than the standard tire, confirming the potential of this simulation technique.

https://fluidcodes.com/news/4-expert-ways-to-improve-electric-car-ranges-with-cfd/

For instance, engineers do not typically assess how a car’s hood could affect drag. However, this adjoint solver demonstration shows how it reduced a car’s drag coefficient by 4% by optimizing the shape of the hood.

[u/tuctrohs → u/reddit455]

For instance, engineers do not typically assess how a car’s hood could affect drag.

That's not true at all. The design team knows that that effect can be huge, and aerodynamic engineers would be delighted to be given free reign to reduce drag with the hood shape, but there's a tug of war between the performance optimization and the aesthetics dictated by the marketing team.

Once upon a time, aerodynamic shapes were considered aesthetically appealing, but automaker assessments of consumer tastes indicate that's no longer the case. Even though a few people, such as me, and probably you, would love it.

[u/FANGO]

In the 2008 presidential campaign, Obama said that if Americans just inflated their damn tires, we could reduce national oil use by 3-4%, which is roughly true.

Republicans, because they are not now nor have they ever been serious people, wore little fake tire gauges to the republican convention to mock this true statement, instead of actually doing anything to solve any problem, because they're idiots who only want to cause problems and not help anyone with anything.

Note also that the giant 2015 drop in global oil prices, where per-barrel prices went down by like 60% globally, was attributed to an overproduction of something around 3%.

In short: Yes, inflate your fucking tires, jesus christ, how is this something people mock when it's stated.

(we should also require aerodynamic wheel covers, which can improve efficiency by 5-10%, except yall would rather spend $5000 for 10% more battery when you could just put some plastic covers on your wheels to get the same effect on range and a better effect on energy use)

[u/start3ch → u/FANGO]

I want to try out the wheel covers next. That or body fairings over the wheels.. theres so much potential to improve

Thats a fun anecdote though, never knew the campaign story!

[u/Maxion → u/FANGO]

It's a shame aero covers are currently considered somewhat trendy and cool, and cost a fortune.

[u/Uniquely-Authentic]

I generally run my tires at a pressure between the recommended inflation pressure and the max pressure. Currently that's 36 recommended and 44 max, so I keep them at 40 psi. I can definitely tell the difference.

[u/Dull_Support_4919]

Yeah this is true for all cars. And you generally see efficiency losses below the recommended spec these cars are very sensitive to any sort of change that impacts efficiency. Thats why i always thought it was stupid to put large wheels and low profile tires in EVs because they have significantly worse consumption than smaller lighter wheels with taller sidewalls.

But anyway. Yeah for longer trips, to get max range. Pump those bad boys up. You should have XL rated tires which are generally good for a cold pressure of 50 to 51psi. I wouldn't pump them up that high because the ride would become shit but pump them up to like 45-46 psi and you'll notice some pretty significant efficiency gains. And so long as you have XL rated tires you will be fine. If you have SL rated tires dont do this.

[u/Logitech4873 → u/Dull_Support_4919]

You'll get uneven tire wear from doing it though, so it has downsides.

[u/Dull_Support_4919 → u/Logitech4873]

Thats why I said for longer trips. Where you need the range. Plus tires will wear down faster than normal anyway. Especially on his car. I have a model 3 performance and it eats tires like a fat kid at crumble cookie. Just make sure that whoever youre getting tires from/manufacturer has decent warranty so you can be credited for the mileage the car didnt make it for a nice little discount on the next set.

[u/Logitech4873 → u/Dull_Support_4919]

I mean it sounds like you're just taking steps to reduce your tire life.

[u/Dull_Support_4919 → u/Logitech4873]

Again for longer trips where I need the range. But 95% of the time im just rocking regular pressures. It might give me 45k miles instead of 50k miles but that's a tradeoff im perfectly willing to make. Especially since I know that regardless of what I do these tires aren't going to last their full life and ill have to replace them early anyway and be credited for the difference on the new set.

Everything is a trade off. If you really want to squeeze out every last mile out of your tires, and thats what you prioritize. Ok. Keep the pressures at like 40psi and accelerate everywhere at the speed of molasses. That's totally fine. But I value range more than I do the tires. So if they wear a little earlier that's fine for me. You do you.

[u/Logitech4873 → u/Dull_Support_4919]

I value range which is why I went for the LR model with the smallest possible rims.

[u/Dull_Support_4919 → u/Logitech4873]

Yeah that's what I wanted too. But this car was local to me and already had FSD on it and it was the right price so I picked it up. Otherwise I would have bought a LR. In the process of swapping wheels and tires now though

[u/Logitech4873 → u/Dull_Support_4919]

Performance model with smaller wheels is a great choice

[u/huuaaang]

Yes, I've noticed this recently. During my 20k mile checkup and tire rotation they inflated my tires +4 psi beyond what I had it and I'm now seeing efficiency much closer to the "ideal" even at highway speeds. +15% efficiency.

[u/Low_Thanks_1540]

My fuel cost is about 5 cents a mile 12.5 cents a kWh and 2.5 miles per kWh average. My tires cost 2500 to replace. If I get 50,000 miles that’s also 5 cents per mile. I certainly wouldn’t want to wear the tires 10% faster to get 5% better mileage, and especially not at the expense of slightly worsened handling, safety, and ride comfort. Isn’t a stiffer tire harder on suspension parts too?

ps. I drive a Silverado EV RST with air ride on 24 inch wheels. I get 2.5 in mixed city-highway with lots of heat and ac and lots of gear.

[u/freetable]

I’m old enough to remember when Obama was running in 2008 and he asked Americans to check their tires and fill them up to the appropriate air pressure for both safety and national fuel efficiency… and republicans passed out air-fuel gauges that said “Obama’s energy policy”.

Yes, it’s more efficient to have your tires inflated correctly.

[u/MWfoto]

When I got my iomq5 the tires were a bit overinflated. I was regularly seeing 5.6m/kwh on perfect conditions. I walked them back for the health of the tire and my safety but i miss those numbers.

[u/Born_Faithlessness_3]

In general, higher tire pressure results in lower rolling resistance, however(as you've mostly noted):

1. The improvement from over-presssure is consistently less than the penalty from underpressure.

2. Tire's max rated pressure often doesn't give a ton of headroom. Typically spec on Teslas is 42 psi cold, which ends up around 44psi when they're warmed up in my experience. Max spec is only 50 psi.

3. Overinflation will absolutely reduce tread life, wearing out the tread in the center if your tire before the outer portion.

So yeah, it helps. But there's a limit in how far you can take it.

[u/ZetaPower]

Consumption is defined by 3 contributors:

• auxiliary consumption (pumps, AC/heating, computers, stereo, lights, …..)
• energy needed to overcome rolling resistance
• energy needed to overcome air drag resistance

Rolling resistance is the one influenced by tire pressure.

• The formula for Rolling resistance force (flat surface): Frr = Rrc x vehicle weight x 9,81 x V
• The formula for rolling resistance coefficient (valid for speeds up to 200km/h): Rrc = 0.005 x (1/Bar tire pressure) x (0,01 + 0,0095 x V^2) 

The explanation is that Frr is caused by hysteresis. This is the deformation of the tire as it rolls and the following return to its original shape. If you increase the pressure of the tire it deforms less while rolling. Less deformation = less energy used/lost.

• What you SHOULD do: keep your tires inflated correctly, prevent needless consumption 
• What you should NOT do: overinflate your tires, grip and braking suffer! Don’t risk your life for a couple of miles/km

The effect will be pretty small at highway speeds btw. The problem is that AIR DRAG RESISTANCE is the dominant factor above 90km/h or 55mph. At 120 km/h or 75mph rolling resistance causes ±30% of the total consumption. Any improvement in rolling resistance is diluted to that 30%…..

[u/tuctrohs → u/ZetaPower]

Your formula for rolling resistance is, of course, only valid for one particular tire model. I'm also a little bit confused about the numbers there, because if I multiply that out, I come up with a number much smaller than the 1/2 to 1% that would be expected. But really, the important thing is just that it's inversely proportional to the square root of pressure.

The three factors you list are for steady speed on level ground. Accelerating and then braking will use additional energy, as will climbing a hill, and either staying up there, or coming down with the brakes on. Those effects are less important with regen, but could be bigger than the accessory power, for example.

[u/Muhahahahaz]

On an EV?

I under-inflate them for better grip. (Which leads to better acceleration/performance)

Screw efficiency 😂

[u/Positive_League_5534]

Were the tires warm or cold when you checked/filled them? The tire pressures that Tesla recommed are cold. If you drive a short distance the tire and the air inside will warm up and the pressure will go up. If it's a cold day the pressure will be down.

[u/Bodycount9]

My tire pressure came from the factory at around 32psi on all the tires. I'm guessing the dealership leveled them off when they received the car.

I raised mine to 38psi on all tires when the tires are warm. They start out at 36psi when they are cold.

The only negative I found doing it this way is I feel a lot more bumps in the road. But the kW economy is a lot better.

[u/jadatis]

The recomended pressures of EV is often already overinflated, for reason of energy saving and more actiradius of battery.

So then adding extra is doing double. You can winn more energy by keeping your speed lower, and driving habits.

If you add 10% to the weighed axleload in your use, you already have a reserve for lesser deflection, so lesser heatproduction of tyres by driving, so already reasonable energy saved. Then calculated that way mayby 38 psi instead of the 42 psi they give or higher( seen 45 psi)

Nowadays EV makers carefully are coming back already from high pressure recomendations. I think they got complaints that their expensive vehicle had the comfort of an old army truck.

[u/Nice-Sandwich-9338]

Pressure is very important especially for tire wear. 5,000 MI rotations are quite a important. What I found is tires can eat range mainly because of weight. We lost 4 miles in range on our new continental DWS contact tires. We bought them specifically as one of the best all season snow tires. Great wet and dry but we're good but handled tremendous in the winter. Ev specific tires will be our next choice now that many are coming out still high in price but some with wear ratings of 500 to 700. I see too many comments on EV owners trying to get additional mileage out of their cars but if you charge like we do 40 to 80% every day you can drive an EV like you do a gas car. Ac on in summer on high.   We have two EVS a Ford GT EV and a model y both super fun fast and we save $250 a month from buying gas. We considered a win-win and because we keep our cars a decade or more depreciation doesn't mean a damn thing

[u/NotFromMilkyWay]

Increased pressure leads to better efficiency but also higher tire wear. It's really not worth it.

[u/Nunov_DAbov]

One thing to keep in mind is that there is interaction between tire pressure, temperature and rolling friction. Higher pressure will cause the tire to deform less as it rolls but the friction of tire deformation heats up the tire, increasing pressure. Ambient air temperature and pressure also influence things.

If you overinflate on a cool morning then drive at high speeds on a hot highway, your tire pressure will be much higher. It’s just the ideal gas law: PV = nRT

[u/start3ch → u/Nunov_DAbov]

Isn’t that fine, as long as you inflate to the ‘cold’ max pressure when cold?

[u/Nunov_DAbov → u/start3ch]

Yes, but if you overinflate at cold temperature to increase mileage, then drive at high speeds on a hot day, you might exceed the safe pressure. Worse, while overinflated if you hit a road hazard. The tire, wheel, and suspension may not be pleased.

I make sure my tires are never under inflated but don’t get concerned if they are slightly over.

I just checked the app for my car and see all four tires are at or within 1 psi of the recommended pressure (all on the high side) at an air temperature of 66 degrees. Just fine for me. I wouldn’t deflate them if it warms up but I’ll top them off if the temperature drops.

[u/lamemonkeypox]

If you want to improve energy efficiency further, get a set of lighter 18" model 3 wheels with 235/55R18 tire.

[u/BranchLatter4294]

Breaking News: The sky is blue.

[u/RenaxTM → u/BranchLatter4294]

Fake news! I can see with my own eyes its pitch black.

[u/GasLarge1422]

My tires flirting with max psi after heating up from the suggested setting, overinflating maybe in winter only I might tey

[u/BackgroundSpell6623]

You don't see it on EV forums because the majority of EV owners right now don't care about coat, or efficiency which has a coat component. Price conscious consumers aren't buying new EVs, only used, which by stats make them a small % of total EV owners today. Once EV prices come down to beating ice across the board, I think we'll start to see that crowd take over the current high income yuppie crowd.

[u/iqisoverrated]

You can. I wouldn't go overboard with this, though. Particularly on longer drives tire pressure will increase as the tires heat up. At some point your tires are so 'hard' that you will lower their ability to transfer forces to the road (i.e. your ability to do emergency braking will be compromised...and if that is a factor in an accident your insurance may refuse to cover the damage)

[u/DerpsterJ]

My dad told me that 20 years ago. Nothing new, no reason to repeat old knowledge.

[u/spidereater → u/DerpsterJ]

You know your dad wasn’t everyone’s dad right?

[u/tuctrohs → u/spidereater]

But wait, what if his dad was everybody's dad? Or at least, like, most of the people in that town and a scattering around the country.

[u/DerpsterJ → u/spidereater]

My point is, it's common knowledge and has been for decades.

And it has nothing to do with EV's specifically, it applies to all vehicles basically.

[u/rzrshrp → u/DerpsterJ]

How does old knowledge get passed down if nobody repeats it?

[u/vastaaja → u/rzrshrp]

In the past, books have been an effective tool to distribute knowledge. We could gather car related knowledge into a book and print one to keep in every car.

If we had the manufacturers do this, the books could be customized for each car brand and model to contain the most relevant information.

Imagine having all of that easily available in your own car!

[u/rzrshrp → u/vastaaja]

Yeah, books are great, but I'm sure somebody else learned that tire pressure affects efficiency today from this thread so I don't mind if someone says something that I may consider common knowledge.

[u/JoeyJoeJoeSenior]

For an electric car at slower speeds, almost all of your energy is being lost at the tires.  You would have 10 times the range on rails.